The claimed invention relates generally to the field of disc drive data storage devices and more particularly, but not by way of limitation, to an improved disc clamp assembly used to secure a number of discs to a spindle motor hub assembly in a disc drive disc stack assembly.
A disc drive is a data storage devices used to store digital data. A typical disc drive includes a number of rotatable magnetic recording discs which are axially aligned and mounted to a spindle motor for rotation at a constant, high speed. A corresponding array of read/write heads access tracks defined on the respective disc surfaces to write data to and to read data from the discs.
A disc clamp assembly is used to clamp the discs (and intervening disc spacers) to a spindle motor hub. The disc clamp assembly applies an axially directed clamping force to the resulting disc stack to secure the discs and spacers to the hub. A greater clamping force generally improves the ability of the disc stack to resist disc shifting in response to the application of mechanical shocks to the disc drive. However, the application of too great a clamping force upon the disc stack can induce undesired mechanical distortion of the discs. Localized variations in the amount of clamping force upon the topmost disc can also induce distortion of the discs.
With the continued industry trend of providing disc drives with smaller overall sizes and greater amounts of data storage capacity, the size of various disc drive components has been reduced, including reductions in the thickness of each disc. As the discs become thinner, the maximum amount of clamping force that can be applied to secure the discs to a spindle motor hub without causing mechanical distortion of the discs is also generally reduced.
Prior art disc clamp assemblies typically engage a feature of the spindle motor to exert the clamping force upon the discs. Such engagement can be accomplished through the use of threaded screws which fasten a clamp member to the spindle motor hub. The desired clamping force is exerted in relation to the torque applied to the screws. Other engagement methodologies have involved the use of interference fits between the clamp member and the spindle hub to wedge or otherwise lock the clamp member in place. These and other prior art disc clamp assemblies can readily generate undesired particulate contamination within the disc drive.
Moreover, during installation of such disc clamp assemblies a large axial force is applied to the spindle motor hub, which can undesirably result in the application of large axially directed forces to ball bearing assemblies used to rotate the spindle motor hub relative to a central shaft. Such forces can deform or otherwise damage the bearing assemblies, inducing runout errors during subsequent rotation of the discs. Such errors become increasingly undesirable with continued increases in track densities in subsequent generations of drives.
Further, prior art disc clamp assemblies can require significant assembly resources to install and correctly set the desired clamping force. Screw-type clamps require insertion and torquing of multiple threaded fasteners; interference-fit type clamps typically require complicated tooling to manipulate the various elements to achieve the final clamping configuration. Subsequent removal of the clamping assembly can also require significant resources and can lead to further generation of particulate contamination.
U.S. Pat. No. 5,101,306 issued to Johnson illustrates such deficiencies with the prior art. Johnson ""306 discloses a rigid grip ring which engages a spindle motor hub. A push-on retaining ring is pressed down over in sliding contact with the grip ring to a final engagement position within a detent of the grip ring, after which the retaining ring bears against the grip ring to apply a clamp force to a disc stack. Johnson ""306 potentially generates significant particulate contamination, requires relatively complicated tooling to install and subsequently remove the retaining ring, and applies significant axially-directed forces upon the spindle motor bearing assemblies during both installation and deinstallation of the retaining ring. Johnson ""306 further appears to require manual (hand) operations to install and deinstall the clamp and is thus not readily adaptable for use in high volume automated assembly environments.
There is a need, therefore, for an improved disc clamp assembly which overcomes these and other deficiencies in the prior art and which applies more consistent and controlled axially directed clamping forces upon the discs and the spindle motor of a disc drive.
A method is provided for forming a disc stack assembly for use in a disc drive.
In accordance with preferred embodiments, the disc stack assembly is formed from a spindle motor hub configured for rotation about a motor axis and having an annular ring recess, at least one disc, and a disc clamp assembly comprising an annular retaining ring and a substantially disc shaped clamp plate. The clamp plate includes an inner ring engagement portion, an outer disc engagement portion, an annular hat flange, and an initial, substantially planar shape in an undeformed state.
The disc stack assembly is preferably formed by loading a number of discs onto the spindle motor hub. The clamp plate is supported adjacent the spindle motor hub so that a portion of the spindle motor hub projects through the central opening of the clamp plate. In this way, the inner ring engagement portion is brought adjacent the annular ring recess and the outer disc engagement portion is brought adjacent the topmost disc.
Next, an axially directed force is applied to the clamp plate at a position adjacent the inner ring engagement portion to conically deform the clamp plate. The retaining ring is installed in the annular ring recess of the spindle motor hub. The axially directed force upon the clamp plate is thereafter removed so that the inner ring engagement portion of the clamp plate applies a first moment force against the retaining ring while the outer disc engagement portion of the clamp plate applies a second moment force as an axially directed clamping force upon the topmost disc as the clamp plate attempts to return to an undeformed state.
Preferably, the annular hat flange is supported to hold the outer disc engagement portion in a clearing, noncontacting relationship with remaining portions of the disc stack assembly so that the axially directed force applied to the clamp plate is not transmitted to the spindle motor hub. Moreover, the outer disc engagement portion is released concurrently with the removal of the axially directed force so that substantially no net axially directed force is applied to the spindle motor hub as the inner ring engagement portion applies the first moment force against the retaining ring and the outer disc engagement portion applies the second moment force to the topmost disc.
The method further preferably comprises steps of measuring imbalance of the assembled disc stack assembly. The measured imbalance is reduced by selectively removing material from the hat flange by cutting recesses in the hat flange. The measured imbalance is alternatively reduced by attachment of a balance weight to the hat flange.
The method further preferably comprises prior steps of providing the clamp plate with a plurality of hook flanges which project from the inner ring engagement portion and placing the retaining ring within said hook flanges prior to placement of the clamp plate and the annular retaining ring on the spindle motor hub.
These and various other features and advantages which characterize the claimed invention will be apparent from a reading of the following detailed description and a review of the associated drawings.